Conventionally, when a mobile station transmits and receives signals to/from a base station in a mobile communication system, the mobile station attempts to establish a connection with the base station by transmitting radio waves of which the transmission power is increased stepwise from an initial value. The mobile station detects that the mobile station has moved from one location registration area to another by, for example, receiving from a base station an identifier of the location registration area having the base station located therein.
When the mobile station detects that the mobile station has moved from one location registration area to another, the mobile station attempts to establish a connection with the base station to transmit to a switching station via the base station, a registration request requesting the switching station to register an identifier of the location registration area having the mobile station located therein. In this case, when plural mobile stations are carried by a transport facility such as a train, the mobile stations pass together a border of location registration areas and therefore, the mobile stations attempt to establish a connection with a base station and consequently, congestion may be caused in the uplink communication of the base station.
For example, according to an existing technique, when a location registration area changes, a random timer is turned on and location registration is requested using the expiration of the random timer as the trigger (see, e.g., Japanese Laid-Open Patent Publication No. 2002-051374). According to another technique, in a case where a location registration regulation signal from a base station is monitored, when location registration is requested to the base station from a location in the location registration regulation area, the location registration request is regulated at a specific probability and the location registration is requested after standing by for a predetermined time period (see, e.g., Japanese Laid-Open Patent Publication No. H04-373328).
According to another technique, when the reception level of a signal sent from a base station is less than or equal to a first threshold value, the transmission power is set to be higher (see, e.g., Japanese Laid-Open Patent Publication No. 2006-101180). According to another technique, an operation information database of a transport facility is referred to, and when the transport facility to passes through the border of a location registration area, the location registration area of mobile terminals loaded on the transport facility is changed (see, e.g., Japanese Laid-Open Patent Publication No. 2004-129119).
Nonetheless, according to the conventional techniques, when access concentrates at the base station consequent to, for example, a commute period, noise in the uplink band becomes significant and access attempts increase. Therefore, congestion of the communication cannot be suppressed.